Rotary lawn mowers and grass cutting blades serving to cut grass or other vegetation are well known in the art today. Typically a grass cutting blade, also referred to as a "cutting bar" is rotated about a generally vertical axis within a downwardly opening housing in order to cut grass by rapid vertical movement of one or more cutting edges defined by the cutting blade. The rotating blade may also include one or more air-fanning "foils" or "vanes" which serve to create air movement into, about, and out of the cutting housing to transport cut clippings either out of a discharge opening (where it can be bagged or broadcast sidewardly away from the housing), or downwardly onto and into the cut grass, where it preferably may be allowed to decompose.
In the instance where the grass clippings (or other cut organic matter such as leaves, weeds, etc.,) are caused to be transported downwardly onto the cut grass, it has been found to be desirable to cut the clippings as finely as possible, and to dispense such grass clippings between the cut grass blades and onto the ground surface. This process, often referenced in the art by descriptive terms such as "mulching", "composting", or "recyling", allows the clippings to decompose with minimal interference with the growing of the cut grass. Upon decomposition, the clippings may nourish the growing grass.
In the prior art, it has been known to provide different cutting blades and blade housing configurations to adapt to the particular type of cutting desired. For example, certain blades have been found to be acceptable for bagging or sidedischarging of clippings, while other blades have been found to be best suited for mulching. However, it is obviously advantageous to provide a single type of blade and accompanying housing which may provide both functions.
Although many different cutting blade configurations are known in the prior art, disadvantages do exist. Some such disadvantages include clogging of the cut grass within the housing or on the blade, due to inadequate cutting of the grass, or inadequate air flow within the blade housing. Other disadvantages include uneven dispersal of the clippings, unacceptable power consumption, and difficulties in resharpening.
U.S. Pat. No. 3,780,509 to Woelffer entitled "Rotary Lawn Mower Cutter Bar Width Bi-Level Cutter", issued Dec. 25, 1973, discloses a grass cutting blade including a pair of cutters on each opposite end of the blade. The pair of cutters includes an upper and lower blade, with the upper blade in rotational advance of the other blade, so that the leading upper cutter will cut the grass prior to being cut by the trailing lower cutter. A air-fanning blade is also provided to create a flow air to convey the clippings from the blade and through the outlet of the mower.
U.S. Pat. No. 2,760,327 to Bovee, entitled "Housing for Disc Type Power Mower", issued Aug. 28, 1956, discloses a lawn mower which includes a pair of cutting blades 31, 30, the upper of which may be in slight rotational advance of the lower blade 30.
U.S. Pat. No. 3,477,214 to Rogers, entitled "Rotor Assembly for a Shredder Implement", issued Nov. 11, 1960, discloses a shredder implement including multiple cutting blades, some of which are vertical spaced from the other and may pivot about their own axis.
U.S. Pat. No. 2,547,540 to Roberts, entitled "Power Mower", issued Apr. 3, 1951, discloses a power mower including a cutter bar 33, itself including multiple cutting blades 36.
U.S. Pat. No. 2,697,322 to Watrous, entitled "Cutter Member for Rotating Disk Type Lawn Mowers", issued Dec. 21, 1954, discloses a power lawn mower including multiple cutting blades such as 15, 16, which may be vertically spaced apart. The cutting blades 15, 16, include corresponding air propelling flanges 18 at their rear margins.
U.S. Pat. No. 2,908,128 to Mauro, entitled "Cutting Device for Rotary Mowers", issued Oct. 13, 1959, discloses a rotary mower including multiple cutting edges.
U.S. Pat. No. 3,703,071 to Anderson, entitled "Rotary Blade for Mulching Lawn Mower", discloses a rotary blade for a power-driven lawn mower which includes an elongate body terminating at each end in a plurality of integral cutting fingers parallel to and displaced successively below and above the plane of the body of the rotary blade.
U.S. Pat. No. 4,318,268 to Szymanis, entitled "Mulching Lawn Mower", discloses a mulching lawn mower which includes a toroidal portion bounded by concentric skirt walls wherein the cross sectional area of the toroid increase towards the inner skirt. A cutting blade 26 is twisted in a particular configuration to provide flipping movement as shown in FIG. 2.
U.S. Pat. No. 4,977,735 to Davis, entitled "Lawn Sculpturing Method and Apparatus", issued Dec. 18, 1990, discloses several grass cutting blades which may be used to provide sculpturing effects in lawns, due to multiple cutting edges at various vertical heights.
U.S. Pat. No. 2,682,142 to Clark, entitled "Cutter Element for Rotary Mowers", issued Jun. 29, 1954, discloses cutting elements in spaced-apart relationships to provide an improved cutting path. FIG. 4 illustrates the interaction of two such cutting blades, one having one cutting edge at each end, and the other having two cutting edges with the upper cutting edge being provide to reduce "streaking", or unmown areas between the adjacent cutter units during turning operations.
U.S. Pat. No. 3,080,697 to Mauro, entitled "Cutting Blade for Rotary Mower", issued Mar. 12, 1963, discloses a lawn mower cutting blade which includes a plurality of cutting edges, such cutting edges in spaced-apart relationships to provide different cutting actions depending on the rotation of the reversible cutting blade.
U.S. Pat. No. 2,857,729 to Zoldok, entitled "Rotary-Type Mower Blade", issued Oct. 28, 1958, discloses a mower blade including not only vertical cutting edges, but also inclined cutting edges.
U.S. Pat. No. 3,538,692 to Cope, entitled "Grass Mowing and Mulching Device", issued Nov. 10, 1970, discloses a grass cutting blade including a plurality of cutting edges. The blade includes not only at each end a horizontal cutting edge 4, as well as a plurality of chopping edges 7, positioned behind the cutting edge 4.
U.S. Pat. No. 4,628,672 to Jones, entitled "Rotary Cutter", issued Dec. 16, 1986, discloses a cutter blade including multiple cutting edges, including slicing edges at the extreme ends of the blade.
U.S. Pat. No. 2,669,084 to Warren, entitled "Rotary Mower Blade", issued Feb. 16, 1954, discloses a cutting blade including vertical pivotable cutting blades 15, each of which include a trailing curved portion 23.
U.S. Pat. No. 2,891,369 to Rietz, entitled "Rotary Shredder and Cutter", issued Jun. 23, 1959, discloses a farmtype implement including a shredder bar member, which includes a downwardly-turned hook 215, sharpened at its leading edge as shown in FIG. 5.
U.S. Pat. No. 3,220,170 to Smith, entitled "Vegetation Mower and Blade", issued Nov. 30, 1975, discloses a cutting blade including cutting edges and an upwardly-turned flanges to provide air flow.
U.S. Pat. No. Re. 32,377 to Seyerle, entitled "Cutter Blade for Pneumatically Transporting Grass Clippings", reissued on Mar. 24, 1987, discloses a cutter blade including an upturned flange for transporting grass clippings.
As may be seen, it is known to provide various cutting blades or cutter bars which include multiple cutting edges and which may include upturned or down turned air foils to provide improved air flow. However, disadvantages do exist in the prior art.
Therefore it may be seen that a need exists for a grass cutting blade which may be used to bag, broadcast, or mulch grass clippings, which cuts the clippings finely. A need also exists for a grass cutting blade which eliminates or minimizes clogging of the clippings on the blade or within the housing, and which provides uniform dispersion of the clippings below the cut grass surface when in its "mulching" mode. A need also exists for a grass cutting blade which is easily made by mass production techniques, and which may be easily resharpened. Finally, a need exists for a grass cutting blade which is efficient in its use of power under a variety of cutting conditions.